Alpha olefin polymer products and catalyst systems

ABSTRACT

The present invention provides a method for varying the melting points and molecular weights of polyolefins by changing the structure of the catalyst used in the polymerization. The catalysts that are useful in the present invention are chiral, stereorigid metallocene catalyst of the formula R″(C 5 R′ m ) 2 MeQ. The catalysts include a bridge structure between the (C 5 R′ m ) groups and may contain substituents on the groups. It has been discovered that the melting points and molecular weights of the polymers produced by such catalysts are influenced by the bridge and substituents added to the (C 5 R′ m ) groups. Thus, the present invention provides a method for varying the melting points of the polymer product and a method of varying the molecular weights of the product by changing the components and structure of the metallocene catalysts. The present invention also provides a process for polymerizing olefins in which the melting points and/or molecular weights of the product may be controlled. Also included in the invention is the discovery that the melting points of the products are controlled by the number of inversions in the xylene insoluble fraction of the polymer.

TECHNICAL FIELD

[0001] The present invention provides a method for varying the meltingpoints and molecular weights of polyolefins in a process ofpolymerization using metallocene catalysts. The catalysts used in thepresent invention are chiral and stereorigid and include a bridgebetween the cyclopentadienyl groups. It has been discovered thatchanging the structure and composition of the bridge leads to changes inthe melting points and molecular weights of the polymer products. It hasalso been discovered that addition of substituents to thecyclopentadienyl rings also influence these polymer properties. Thepresent invention also includes the ability to control the meltingpoints of polyolefins, particularly polypropylene, by controlling thenumber of inversions in the xylene insoluble fraction of the polymerchain.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to the use of metallocene catalystsin the production of polyolefins, particularly polypropylene, and theability to vary certain properties of the polymer products by varyingthe structure of the catalyst. In particular, it has been discoveredthat changes in the structure and composition of a bridge linking twocyclopentadienyl groups in the metallocene catalyst changes the meltingpoints and the molecular weights of the polymer products.

[0003] The use of metallocenes as catalysts for the polymerization ofethylene is known in the art. German patent application 2,608,863discloses a catalyst system for the polymerization of ethyleneconsisting of bis(cyclopentadienyl)-titanium dialkyl, an aluminumtrialkyl and water. German patent application 2,608,933 discloses anethylene polymerization catalyst system consisting of zirconiummetallocenes of the general formula (cyclopentadienyl)_(n) Zr Y_(4-n),wherein Y represents R₁CH₂AlR₂, CH₂CH₂AlR₂ and CH₂CH (AlR₂)₂ wherein Rstands for an alkyl or metallo alkyl, and n is used a number within therange 1-4; and the metallocene catalyst is in combination with analuminum trialkyl cocatalyst and water.

[0004] The use of metallocenes as a catalyst in the copolymerization ofethylene and other alpha-olefins is also known in the art. U.S. Pat. No.4,542,199 to Kaminsky, et al. discloses a process for the polymerizationof olefins and particularly for the preparation of polyethylene andcopolymers of polyethylene and other alpha-olefins. The disclosedcatalyst system includes a catalyst of the formula(cyclopentadienyl)₂MeRHal in which R is a halogen, a cyclopentadienyl ora C₁-C₆ alkyl radical, Me is a transition metal, in particularzirconium, and Hal is a halogen, in particular chlorine. The catalystsystem also includes an aluminoxane having the general formulaAl₂OR₄(Al(R)—O)_(n) for a linear molecule and/or (Al(R)—O)_(n+2) for acyclic molecule in which n is a number from 4-20 and R is a methyl orethyl radical. A similar catalyst system is disclosed in U.S. Pat. No.4,404,344.

[0005] U.S. Pat. No. 4,530,914 discloses a catalyst system for thepolymerization of ethylene to polyethylene having a broad molecularweight distribution and especially a bimodal or multimodal molecularweight distribution. The catalyst system is comprised of at least twodifferent metallocenes and an alumoxane. The patent disclosesmetallocenes that may have a bridge between two cyclopentadienyl ringswith the bridge serving to make the rings stereorigid. The bridge isdisclosed as being a C₁-C₄ alkylene radical, a dialkyl germanium orsilicon, or an alkyl phosphine or amine radical.

[0006] European Patent Application 0185918 discloses a stereorigid,chiral metallocene catalyst for the polymerization of olefins. Thebridge between the cyclopentadienyl groups is disclosed as being alinear hydrocarbon with 1-4 carbon atoms or a cyclical hydrocarbon with3-6 carbon atoms. The application discloses zirconium as the transitionmetal used in the catalyst, and linear or cyclic alumoxane is used as aco-catalyst. It is disclosed that the system produces a polymer productwith a high isotactic index.

[0007] It is known by those skilled in the art that polyolefins, andprincipally polypropylene, may be produced in various forms: isotactic,syndiotactic, atactic and isotactic stereoblock. Isotactic polypropylenecontains principally repeating units with identical configurations andonly a few erratic, brief inversions in the chain. Isotacticpolypropylene may be structurally represented as

[0008] Isotactic polypropylene is capable of forming a highlycrystalline polymer with crystalline melting points and other desirablephysical properties that are considerably different from the samepolymer in an amorphous, or noncrystalline, state.

[0009] A syndiotactic polymer contains principally units of alternatingconfigurations and is represented by the structure

[0010] A polymer chain showing no regular order of repeating unitconfigurations is an atactic polymer. In commercial applications, acertain percentage of atactic polymer is typically produced with theisotactic form. It is highly desirable to control the atactic form at arelatively low level.

[0011] A polymer with recurring units of opposite configuration is anisotactic stereoblock polymer and is represented by

[0012] This latter type, the.stereoblock polymer, has been successfullyproduced with metallocene catalysts as described in U.S. Pat. No.4,522,982.

[0013] It may also be possible to produce true block copolymers ofisotactic and atactic forms of polyolefins, especially polypropylene.

[0014] A system for the production of isotactic polypropylene using atitanium or zirconium metallocene catalyst and an alumoxane cocatalystis described in “Mechanisms of Stereochemical Control in PropylenePolymerization with Soluble Group 4B Metallocene/MethyalumoxaneCatalysts,” J. Am. Chem. Soc., Vol. 106, pp. 6355-64, 1984. The articleshows that chiral catalysts derived from the racemic enantiomers ofethylene-bridged indenyl derivatives form isotactic polypropylene by theconventional structure predicted by an enantiomorphic-sitestereochemical control model. The meso achiral form of theethylene-bridged titanium indenyl diastereomers and the meso achiralzirconocene derivatives, however, produce polypropylene with a purelyatactic structure.

[0015] Further studies on the effects of the structure of a metallocenecatalyst on the polymerization of olefins was reported in “CatalyticPolymerization of Olefins,” Proceedings of the International Symposiumon Future Aspects of Olefin Polymerization, pp. 271-30 92, published byKodansha Ltd., Tokyo, Japan, 1986. In this article, the effects of thechiralities, steric requirements and basicities of ligands attached tosoluble titanium and zirconium metallocene catalysts on thepolymerization and copolymerization of propylene and ethylene werereviewed. The studies revealed that the polymerization rates andmolecular weights of the polymers obtained in the polymerization ofethylene with a zirconocene catalyst vary according to the basicity andsteric requirements of the cyclopentadienyl groups. The effects ofligands also contributed to the synthesis of )olypropylenes with novelmicrostructures and high density polyethylenes with narrow and bimodalmolecular weight distributions.

[0016] The present invention relates to discoveries made as to varryingthe bridge structure and substituents added to the cyclopentadienylrings in a metallocene catalyst on the polymerization of propylene andhigh alpha-olefins. In particular, it was discovered that by varyingthese components, the physical properties of the polymer may becontrolled.

SUMMARY OF THE INVENTION

[0017] As part of the present invention, it was further discovered thatthe number of inversions in the xylene insoluble fraction may be variedby changing the components that form the bridge between thecyclopentadienyl rings in a metallocene catalyst. It was also discoveredthat the addition of various substituents on the cyclopentadienyl ringsalso varied the number of inversions. Thus, a means for varying themelting point of a polyolefin was discovered. This is a significantdiscovery, as heretofore it was the commercial practice to vary themelting points of polymer products by co-polymerizing varying amounts ofethylene to produce co-polymers with a range of differing meltingpoints. It is desirable to produce a homopolymer with varying meltingpoints without the use of ethylene; The present invention provides amethod for the production of homo-polymers with varying melting pointsby varying the structure of the metallocene catalyst used in thepolymerization.

[0018] Similarly, it was discovered that by changing the structure ofthe metallocene catalyst, polymers are produced with varying molecularweights. Thus, the molecular weight of the polymer product may be variedby changing the catalyst. Accordingly, the present invention provides amethod for varying both the melting point and the molecular weight of apolymer product.

[0019] The present invention also provides a process for thepolymerization of olefins comprising contacting an organoaluminumcompound with a metallocene described by the formula:

R″(C₅R′_(m))₂Me Q_(p)

[0020] wherein (C₅R′_(m)) is a cyclopentadienyl or substitutedcyclopentadienyl ring; R′ is a hydrogen or a hydrocarbyl radical havingfrom 1-20 carbon atoms, each R′ may be the same or different; R″ forms abridge between the two (C₅R′_(m)) rings and contains a bridge groupconsisting of an alkylene radical having 1-4 carbon atoms, a siliconhydrocarbyl compound, a germanium hydrocarbyl compound, an alkylphosphine, an alkyl amine, a boron compound or an aluminum compound, andany of these bridge groups may contain any of these or other hydrocarbylgroups attached to the bridge; Q is a hydrocarbon radical such as analkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbonatoms or is a halogen; Me is a group 4b, 5b or 6b metal as positioned inthe Periodic Table of Elements; 0≦m≦4; and 0≦p≦3. An olefin monomer isadded to the metallocene catalyst and the organoaluminum compound. Afterthe polymerization has taken place, the polymer product is withdrawn.The process is characterized by the fact that it provides control of themelting point of the polymer product by controlling the number ofinversions in the xylene insoluble fraction of the polymer. The numberof inversions are effected by the R″ group and the R′ group. Thus, themelting point of the polymer product may be varied and controlled byvarying the R″ bridge and/or the R′ substituents on the cyclopentadienylrings.

[0021] The present invention also provides a method for varying themelting points of polymer products and a method for varying themolecular weights of the polymer products. These methods include the useof the metallocene catalyst described by the above formula. The meltingpoints and molecular weights of the polymer products are varied bychanging the R″ bridge and/or the R′ substituents on thecyclopentadienyl rings.

DETAILED DESCRIPTION

[0022] The present invention provides a method of controlling themelting point of a polymer by controlling the number of inversions inthe chain of the xylene insoluble fraction of the polymers. The numberof inversions are controlled in turn by the structure and composition ofthe catalyst, and the number of inversions and hence the melting pointof the polymer product may be controlled and varied by varying thecatalyst. In particular, it has been discovered that varying tae R″bridge between the cyclopentadienyl rings will vary the melting point ofthe polymer product. Varying the R′ substituents on the rings will alsovary the melting point. In addition, it has been discovered that varyingthe R″ bridge and/or the R′ substitutents in the catalyst will also varythe molecular weights of the polymer products. These beneficialadvantages will become more apparent from the following detaileddescription of the invention and the accompanying examples.

[0023] Normally, when propylene, or another alpha-olefin, is polymerizedin a catalyst system prepared from a transition metal compound, thepolymer comprises a mixture of amorphous atactic and crystalline xyleneinsoluble fractions which may be extracted using suitable solvents.Transition metal catalysts in the form of metallocenes have been knownfor some time, but up until just recently, such catalysts could onlyproduce predominantly atactic polymer which is not nearly as useful asthe isotactic form. It was discovered that by attaching a bridge betweenthe cyclopentadienyl rings in a metallocene catalyst and by adding oneor more substituents on the rings to make the compound both stereorigidand chiral, a high percentage of isotactic polymer could be produced. Asdescribed by the present invention, the composition of the bridge andthe substituents added to the rings affect the properties of the polymersuch as melting points and molecular weights.

[0024] The metallocene catalyst as used in the present invention must bechiral and stereorigid. Rigidity is achieved by an interannular bridge.The catalyst may be described by the formula:

R″(C₅R′_(m))₂ Me Q_(p)

[0025] wherein (C₅R′_(m)) is a cyclopentadienyl or substitutedcyclopentadienyl ring; R′ is a hydrogen or a hydrocarbyl radical havingfrom 1-20 carbon atoms, each R′ may be the same or different; R″ is thebridge between the two (C₅R′_(m)) rings and is an alkylene radicalhaving 1-4 carbon atoms, a silicon hydrocarbyl compound, a germaniumhydrocarbyl compound, an alkyl phosphine, or an alkyl amine; Q is ahydrocarbon radical such as an alkyl, aryl, alkenyl, alkylaryl orarylalkyl radical having 1-20 carbon atoms or is a halogen; Me is agroup 4b, 5b or 6b metal as positioned in the Periodic Table ofElements; 0≦m≦4; and 0≦p≦3.

[0026] Exemplary hydrocarbyl radicals are methyl, ethyl, propyl, butyl,amyl, isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl,phenyl, and the like. Exemplary alkylene radicals are methylene,ethylene, propylene and the like. Exemplary halogen atoms includechlorine, bromine and iodine with chlorine being preferred.

[0027] The preferred transition metals are titanium, zirconium andhafnium. Q is preferably a halogen and p is preferably 2. R′ ispreferably a phenyl or cyclohexyl group such that (C₅R′_(m)) forms anindenyl radical which may be hydrated. As indicated, other hydrocarbongroups may be added to the cyclopentadienyl rings. The preferred R″bridge components are methylene (—CH₂—), ethylene (—C₂H₄—), an alkylsilicon and a cycloalkyl silicon such as cyclopropyl silicon, amongothers. The present invention is such that the R″ bridge and the R′substituents may be varied among any of those compounds listed in theabove formula so as to provide polymer products with differentproperties.

[0028] The metallocene catalysts just described are used in combinationwith an organoaluminum compound. Preferably, the organoaluminum compoundis an alumoxane represented by the general formula (R—Al—O) in thecyclic form and R(R—Al—O—)_(n)AlR₂ in the linear form. In the generalformula, R is an alkyl group with 1-5 carbons and n is an integer from 1to about 20. Most preferably, R is a methyl group. Generally, in thepreparation of alumoxanes from, for example, trimethyl aluminum andwater, a mixture of the linear and cyclic compounds are obtained.

[0029] The alumoxanes can be prepared in various ways. Preferably, theyare prepared by contacting water with a solution of trialkyl aluminum,such as, for example, trimethyl aluminum, in a suitable solvent such asbenzene. Most preferably, the alumoxane is prepared in the presence of ahydrated copper sulfate as described in U.S. Pat. No. 4,404,344 thedisclosure of which is hereby incorporated by reference. This methodcomprises treating a dilute solution of trimethyl aluminum in, forexample, toluene with copper sulfate represented by the general formulaCuSO₄.5H₂O. The reaction is evidenced by the production of methane.

[0030] The metallocene catalysts used in the present invention areproduced using methods known to those skilled in the art. Typically, theprocedures simply comprise the addition of the MeQ groups describedabove and the R″ group to a starting compound such as indene or someother substituted dicyclopentadiene.

[0031] The polymerization procedures useful in the present inventioninclude any procedures known in the art. An example of a preferredprocedure would be that disclosed in co-pending application Ser. No.009,712, hereby incorporated by reference which describes apre-polymerization of the catalyst before introducing the catalyst intoa polymerization reaction zone.

[0032] In the Examples given below, three different polymerizationprocedures were utilized. These procedures, designated as A, B and C aredescribed as follows:

Procedure A

[0033] A dry two liter stainless steel Zipperclave was utilized as thereaction vessel and was purged with 2 psig of nitrogen. An alumoxanesolution was introduced into the reaction vessel using a syringe whichwas followed by the introduction of the metallocene catalyst solution bya second syringe. Approximately, 1.2 liters of propylene are added atroom temperature and then heated to the run temperature in 2-5 minuteswas then added to the reaction vessel, and the agitator was set at 1200rpm. The temperature of the reaction vessel was maintained at the runtemperature. After 1 hour of stirring, the agitator was stopped, thepropylene was vented, and 500 ml of either heptane or toluene was addedusing nitrogen pressure. The reactor was stirred for 5 minutes and thenthe contents were poured into a beaker containing 300 ml of a 50/50solution of methanol/4N HCl. After stirring for 30 minutes, the organiclayer was separated, washed 3 times with distilled water, and pouredinto an evaporating dish. After evaporating the solvent, the remainingpolymer was further dried in a vacuum oven.

Procedure B

[0034] The procedure is similar to Procedure A except that 1.0 liter ofpropylene was first added to the reactor. The alumoxane and catalystwere added to a 75 cc stainless steel sample cylinder and allowed toprecontact for several minutes before being flushed to the reactor with0.2 liters of propylene. The remaining procedures were as described inA.

Procedure C

[0035] Into a dry 500 cc stainless steel Zipperclave was added 120 cc ofdry toluene and the temperature set at the designated run temperature.The alumoxane solution was syringed into the reactor followed by theaddition of the catalyst solution by syringe. About 120 cc of propylenewas then added to the reactor using nitrogen pressure. After one hour ofagitation and temperature control, the agitator was stopped and thepropylene vented. The polymer was then extracted as described in A.

[0036] These are just examples of possible polymerization procedures asany known procedure may be used in practicing the present invention.

[0037] The polymer product may be analyzed in various ways for differingproperties. Particularly pertinent to the present invention are analysesfor melting points, molecular weights, and inversions in the chain.

[0038] The melting points in the examples below were derived from DSC(Differential Scanning Calorimetry) data as known in the art. Themelting points reflected in the tables are not true equilibrium meltingpoints but are DSC peak temperatures. With polypropylene it is notunusual to get an upper and a lower peak temperature, i.e., two peaks,and the data reflects the lower peak temperature. True equilibriummelting points obtained over a period of several hours would be 5-12° C.higher than the DSC lower peak melting points. The melting points forpolypropylenes are determined by the crystallinity of the xyleneinsoluble fraction of the polymer. This is shown to be true by runningthe DSC melting points before and after removal of the xylene solublesor atactic form of the polymer. The results showed only a difference of1-2° C. in the melting points after most of the atactic polymer wasremoved and isotactic polymer remained. The xylene insoluble fraction ofthe polymer yields a sharper and more distinct melting point peak.

[0039] NMR analysis was used to determine the exact microstructure ofthe polymer including the mole fraction of inversions in the chain ofthe xylene insoluble fraction. The NMR data may be actually observed orit may be calculated using statistical models. NMR analysis is used tomeasure the weight percent of atactic polymer and the number ofinversions in the xylene insoluble fraction of the polymer.

[0040] The molecular weights of the xylene insoluble fractions of thepolymers were calculated using GPC (Gel Permeation Chromatography)analysis. For the examples given below, the analysis was done on aWaters 150 C instrument with a column of Jordi gel and an ultra highmolecular weight mixed bed. The solvent was trichlorobenzene and theoperating temperature was 140° C. From GPC, M_(w), or the weight averagemolecular weight, and Mn are obtained. M_(w) divided by M_(n) is ameasurement of the breadth of the molecular weight distribution.

[0041] As known in the art, the molecular weight of a polymer isproportional to the rate of propogation of the polymer chain divided bythe rate of termination of the chain. A change in the ratio leads to achange in the molecular weights. As described by the present invention,a change in the structure of the catalyst leads to a change in the ratioof the rates of polymerization as well as a change in the melting pointsof the polymer.

[0042] The following Examples illustrate the present invention and itsvarious advantages in more detail. The Examples use various zirconocenesto illustrate the invention but similar results would be expected usingtitanocene, hafnocenes and other metallocene catalysts. The results aresummarized in Table 1.

EXAMPLE 1

[0043] The polymerization of propylene was carried out using 3 mg ofethylenebis(indenyl)zirconium dichloride as the catalyst and usingpolymerization Procedure B as outlined above. Enough alumoxane was usedto produce a Al/Zr metal atom ratio of 1.4 mol 10 Al/mmol of Zr. Thereaction temperature was 30° C. The polymerization produced a yield of51.0 grams of polypropylene which results in an efficiency of 17.0 kg ofpolypropylene/g of catalyst in 1 hour (kg/g.cat.1h). Atactic polymer wasremoved by dissolving the polymer product in hot xylene, cooling thesolution to 0° C., and precipitating out the isotactic form. Theintrinsic viscosity of the xylene insoluble fraction was calculated tobe 0.495 dl/gm from measurements taken on a Differential Viscometer indecalin at 135° C. The GPC analysis showed a M_(w) of 40,000 and aM_(w)/M_(n) of 2.2 for the xylene insoluble or xylene insolublefraction. The results are summarized in Table 1.

EXAMPLE 2

[0044] Polymerization Procedure C as described above was used with 2.00mg of ethylenebis(indenyl)zirconium dichloride as the catalyst. TheAl/Zr ratio was 2.1 (mol/mmol) and the reaction temperature was 50° C.In addition to the analyses performed in Example 1, DSC analysis for apeak temperature or melting point (T_(m)) of the xylene insolublefraction and analysis of the NMR spectrum for the mole fraction ofinversions in the isotaction fraction in the chain were performed. Theresults are shown in Table 1.

EXAMPLE 3

[0045] Polymerization Procedure A as described above was used with 0.6mg of ethylenebis(indenyl)zirconium dichloride as the catalyst. TheAl/Zr ratio was 7.0 (mol/mmol) and the reaction temperature was 50° C.The results of the polymerization and analysis are shown in Table 1.

EXAMPLE 4

[0046] The procedures of Example 3 were repeated except that 1.43 mg ofcatalyst were used, the Al/Zr ratio was 2.9 (mol/mmol) and the reactiontemperature was 80° C. A tremendous increase in the yield and efficiencyof the catalyst were obtained. The results are shown in Table 1.

EXAMPLES 5-8

[0047] In these Examples, the catalyst used wasethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, thetetrahydrated form of the catalyst used in Examples 1-4. This was donein order to demonstrate the effect of a different substituent on thecyclopentadienyl rings. The polymerization runs were carried out usingvarying procedures, catalyst amounts, Al/Zr ratios, and temperatures asindicated in Table 1. The results in Table 1 show a different range ofmelting points (T_(m)) and molecular weights (M_(w)) as the catalyst washydrogenated.

EXAMPLES 9-11

[0048] These Examples used a zirconocene catalyst with a dimethylsilicon bridge instead of an ethylene bridge. The catalyst used wasdimethylsilylbis(indenyl)zirconium dichloride. The polymerizationconditions and results are shown in Table 1. With the substitution of asilicon bridge for an ethylene bridge, the melting points and molecularweights increased.

EXAMPLES 12-17

[0049] These Examples used a catalyst with a cyclopropyl group attachedto a silicon bridge—thus the catalyst wascyclopropylsilylbis(indenyl)zirconium dichloride. The polymerizationconditions and results are shown in Table 1. Slightly higher meltingpoints and molecular weights were obtained with this structure ofcatalyst.

EXAMPLE 18

[0050] In this example, a zirconocene catalyst with a larger bridgestructure was used; the catalyst used was1,1,4,4,-tetramethyl-disilylethylenebis(indenyl)zirconium dichloride inthe amount of 1.45 mg. The Al/Zr ratio was. 6.0 mol/mmol and thereaction temperature was 50° C. The reaction was run for an hour, but nosignificant amount of polypropylene was formed. In other tests, thiscatalyst was shown useful in the polymerization of ethylene and acopolymer of ethylene and propylene. TABLE 1 Mole Percent of InversionsPoly. Al/Zr Yield Efficiency Tm ° C. in Isotactic I.V. Example Proc.Cat. mg. mol/mmol Temp. ° C. gms kg/g. cat. 1 h DSC Peak Fraction dl/gmMw/1000 Mw/Mn 1 B 3.0 1.4 30 51.0 17.0 140 0.50 40 2.2 2 C 2.0 2.1 5020.0 12.7 135.2 2.5 0.23 3 A 0.6 7.0 50 25.4 33.3 135.3 0.33 23 2.2 4 A1.43 2.9 80 221.0 154.5 125.6 4.5 0.23 14 2.1 5 A 19.6 0.2 20 16.5 0.8143.0 1.2 0.39 6 B 49.9 0.1 10 13.0 0.3 139.7 0.42 29 3.5 7 A 1.86 2.350 33.0 17.7 136.8 0.18 11 2.3 8 A 3.38 1.3 80 265.0 78.4 120.9 0.10 9 A3.5 1.3 30 8.7 2.5 145.2 0.61 50 2.2 10 C 2.0 2.2 50 64.0 32.0 142.3 1.60.46 36 2.3 11 A 0.7 6.4 80 20.5 29.3 135.3 3.1 0.27 18 2.2 12 B 10.00.5 30 1.8 0.2 146.7 0.41 13 B 1.0 4.6 30 6.0 6.0 0.55 14 B 3.1 1.5 501.8 0.6 141.5 0.40 30 3.4 15 B 1.0 4.6 50 14.0 14.0 0.48 16 A 2.89 1.680 5.8 2.0 138.2 0.36 26 2.7 17 B 2.50 1.8 80 69.0 27.6 0.41 18 B 1.456.0 50 0 0

[0051] The results shown in Table 1 illustrate some of the advantages ofthe present invention. The substituents on the cyclopentadienyl ringsand the compositions and structures of the bridge between the rings dohave a significant influence on the stereoregularities, melting pointsand the molecular weights of the polymers. These effects are a result ofthe steric and electronic properties of the substituents and bridgestructures.

[0052] It is noted that the polymerization temperature is a factor inthe formation of the polymer product. At the lower reactiontemperatures, the melting points and molecular weights for the samecatalyst were higher. As the reaction temperatures increased, themelting points and the molecular weights decreased. Also, as thereaction temperature increased, the yields and catalyst efficienciesalso increased, usually dramatically.

[0053] Some of the advantages of the present invention are realized bycomparing the polymer properties of Examples using different catalystsbut run at the same polymerization temperature. In making thesecomparisons, it can be seen that the melting points increased and themole fraction of inversions decreased as the R″ bridge structure waschanged from ethylene to an alkyl silicon bridge. The molecular weightsalso increased as silicon was substituted for ethylene. The results showthat polymers with lower molecular weights are produced by catalystswith more bulky and more basic ligands. Also, some increase was noted asthe indenyl groups were hydrated. Thus, the more electron dontaing thatthe R′ and R″ groups are, the molecular weights of the products can beexpected to be higher. The results clearly show that the melting pointsand molecular weights can be varied by changing the bridge structure andthe substituent groups in the cyclopentadienyl rings.

[0054] Example 18 illustrates a limit to the number of atoms forming theR″ bridge. Apparently, the steric effect of inserting two carbon atomsand two alkyl silicon groups was too great and caused the catalyst toshift in such a way as to block the production of propylene.

[0055] It is known that the mole fraction of inversions in the isotacticpolymer chain does correlate with the melting points. When the molefractions are plotted against the log T_(m), the points fit a straightline through the regions tested in the Examples. The equation for theline is mole fraction of inversions=−0.5 log T_(m)(° C.)+1.094. As thenumber of inversions increase, the melting point of the polymerdecreases. The number of inversions also vary as the R″ bridge ischanged.

[0056] Having described a few embodiments of the present invention, itwill be understood by those skilled in the art that modifications andadoptions may be made without departing from the scope of the presentinvention.

1. In a process for the polymerization of olefins, a method forcontrolling the melting point of a polyolefin, said method comprising:(a) controlling the number of inversions in the chain of the xyleneinsoluble fraction of the polyolefin during the polymerization of olefinmonomer; (b) contacting an organoaluminum compound with a metallocenecatalyst described by the formula: R″(C₅R′_(m))₂Me Q_(p) wherein(C₅R′_(m)) is a cyclopentadienyl or substituted cyclopentadienyl; R′ ishydrogen or hydrocarbyl radical having from 1 to 20 carbon atoms, eachR′ may be the same or different; R″ is an alkylene radical having 1-4carbon atoms, a silicon hydrocarbyl compound, a germanium hydrocarbylcompound, an alkyl phosphine, or an alkyl amine, and R″ acts to bridgethe two (C₅R′_(m)) rings; Q is a hydrocarbon radical such as an aryl,alkyl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atomsor is a halogen; Me is a group 4b, 5b or 6b metal as designated in thePeriodic Table of Elements; 0≦m≦4; and 0≦p≦3; and (c) contacting anolefin monomer with said catalyst and said aluminum compound eithersimultaneously with or after step (b).
 2. A polyolefin produced by theprocess comprising: (a) controlling the number of inversions in thechain of the xylene insoluble fraction of the polyolefin during thepolymerization of olefin monomer; (b) contacting an organoaluminumcompound with a metallocene catalyst described by the formula:R″(C₅R′_(m))₂Me Q_(p) wherein (C₅R′_(m)) is a cyclopentadienyl orsubstituted cyclopentadienyl; R′ is hydrogen or hydrocarbyl radicalhaving from 1 to 20 carbon atoms, each R′ may be the same or different;R″ is an alkylene radical having 1-4 carbon atoms, a silicon hydrocarbylcompound, a germanium hydrocarbyl compound, an alkyl phosphine, or analkyl amine, and R″ acts to bridge the two (C₅R′_(m)) rings; Q is ahydrocarbon radical such as an aryl, alkyl, alkenyl, alkylaryl orarylalkyl radical having 1-20 carbon atoms or is a halogen; Me is agroup 4b, 5b or 6b metal as designated in the Periodic Table ofElements; 0≦m≦4; and 0≦p≦3; and (c) contacting an olefin monomer withsaid catalyst and said aluminum compound either simultaneously with orafter step (b).
 3. A process for the polymerization of olefinscomprising: (a) contacting an organoaluminum compound with a metallocenecatalyst described by the formula: R″(C₅R′_(m))₂Me Q_(p) wherein(C₅R′_(m)) is a cyclopentadienyl or substituted cyclopentadienyl; R′ ishydrogen or hydrocarbyl radical having from 1 to 20 carbon atoms, eachR′ may be the same or different; R″ is an alkylene radical having 1-4carbon atoms, a silicon hydrocarbyl compound, a germanium hydrocarbylcompound, an alkyl phosphine, or an alkyl amine, and R″ acts to bridgethe two (C₅R′_(m)) rings; Q is a hydrocarbon radical such as an aryl,alkyl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atomsor is a halogen; Me is a group 4b, 5b or 6b metal as designated in thePeriodic Table of Elements; 0≦m≦4; and 0≦p≦3; (b) contacting an olefinmonomer with the metallocene catalyst and the organoaluminum compoundeither simultaneously with or after (a); and (c) withdrawing a polymerproduct, wherein the process provides control of the melting point ofthe polymer product by controlling the number of inversions in thexylene insoluble fraction of the polymer during polymerization, and themelting point of the polymers may be varied by varying the R′ or R″groups on the metallocene catalyst.
 4. The process of claim 3 whereinthe metallocene catalyst is a zirconocene.
 5. The process of claim 3wherein the metallocene catalyst is a titanocene.
 6. The process ofclaim 3 wherein the R″ bridge of the metallocene catalyst is an alkylsilicon compound.
 7. The process of claim 3 wherein the organoaluminumcompound is an alumoxane.
 8. The process of claim 3 wherein the olefinmonomer is propylene.
 9. The process of claim 3 wherein the number ofinversions in the xylene insoluble fraction are controlled by the R″group in the metallocene catalyst.
 10. The process of claim 3 whereinthe number of inversions in the xylene insoluble fraction are controlledby the R′ groups attached to the cyclopentadienyl rings.
 11. A methodfor controlling the melting point of an olefinic polymer produced in thepresence of a chiral, stereorigid metallocene catalyst having aninterannular bridge, comprising varying the structure of said bridge.12. The method of claim 11 wherein the metallocene catalyst is describedby the formula: R″(C₅R′_(m))₂Me Q_(p) wherein (C₅R′_(m)) is acyclopentadienyl or substituted cyclopentadienyl; R′ is hydrogen orhydrocarbyl radical having from 1 to 20 carbon atoms, each R′ may be thesame or different; R″ is an alkylene radical having 1-4 carbon atoms, asilicon hydrocarbyl compound, a germanium hydrocarbyl compound, an alkylphosphine, or an alkyl amine, and R″ is a bridge between the two(C₅R′_(m)) rings; Q is a hydrocarbon radical such as an aryl, alkyl,alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is ahalogen; Me is a group 4b, 5b or 6b metal designated in the PeriodicTable of Elements; 0≦m≦4; and 0≦p≦3.
 13. The method of claim 12 whereinthe R″ bridge is varied to include a silicon atom in the bridge.
 14. Themethod of claim 12 wherein the R″ bridge is varied to include an alkylsilicone compound.
 15. The method of claim 12 wherein the R″ bridge ischanged to include an alkylene compound.
 16. The method of claim 12wherein the metallocene catalyst is selected from the group consistingof titanocene, zirconocene, and hafnocene.
 17. The method of claim 12wherein the olefin monomer is propylene.
 18. The method of claim 12further comprising changing the R′ group attached to thecyclopentadienyl rings in the metallocene catalyst.
 19. A method forcontrolling the molecular weight of an olefinic polymer produced in thepresence of a chiral, stereorigid metallocene catalyst havinginterannular bridges comprising varying the structure of said bridge.20. The method of claim 19 wherein said metallocene catalyst isdescribed by: R″(C₅R′_(m))₂Me Q_(p) wherein (C₅R′_(m)) is acyclopentadienyl or substituted cyclopentadienyl; R′ is hydrogen orhydrocarbyl radical having from 1 to 20 carbon atoms, each R′ may be thesame or different; R″ is an alkylene radical having 1-4 carbon atoms, asilicon hydrocarbyl compound, a germanium hydrocarbyl compound, an alkylphosphine, or an alkyl amine, and R″ is a bridge between the two(C₅R′_(m)) rings; Q is a hydrocarbon radical such as an aryl, alkyl,alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is ahalogen; Me is a group 4b, 5b or 6b metal designated in the PeriodicTable of Elements; 0≦m≦4; and 0≦p≦3.
 21. The method of claim 19 whereinthe metallocene catalyst is selected from the group consisting oftitanocene, zirconocene, and hafnocene.
 22. The method of claim 19wherein the bridge is changed to include a silicon atom in the bridge.23. The method of claim 19 wherein the bridge is changed to include analkyl silicon compound.
 24. The method of claim 20 wherein the(C₅R′_(m)) is an indene.
 25. The method of claim 20 wherein the R″bridge is changed to include an alkylene compound.
 26. The method ofclaim 20 further comprising changing the R′ group.
 27. A method forvarying the melting point of a polyolefin in the polymerization of anolefin monomer, said methed comprising: (a) utilizing an organoaluminumcompound, a metallocene catalyst and an olefin monomer in apolymerization reaction, said metallocene catalyst being stereorigid,chiral and described by the formula: R″(C₅R′_(m))₂Me Q_(p) wherein(C₅R′_(m)) is a cyclopentadienyl or substituted cyclopentadienyl; R′ ishydrogen or hydrocarbyl radical having from 1 to 20 carbon atoms, eachR′ may be the same or different; R″ is an alkylene radical having 1-4carbon atoms, a silicon hydrocarbyl compound, a germanium hydrocarbylcompound, an alkyl phosphine, or an alkyl amine, and R″ is a bridgebetween the two (C₅R′_(m)) rings; Q is a hydrocarbon radical such as anaryl, alkyl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbonatoms or is a halogen; Me is a group 4b, 5b or 6b metal designated inthe Periodic Table of Elements; 0≦m≦4; and 0≦p≦3; and (b) changing theR′ group on the cyclopentadienyl rings.
 28. The method of claim 27wherein R′ is changed to include hydrogen.
 29. The method of claim 27wherein the metallocene catalyst is zirconocene.
 30. The method of claim27 wherein the olefin monomer is propylene.
 31. The method of claim 27wherein the metallocene catalyst is hafnocene.
 32. A method for varyingthe molecular weights of a polyolefin in the polymerization of an olefinmonomer, said method comprising: (a) utilizing a metallocene catalyst,an organoaluminum compound and an olefin monomer, said catalyst being ofthe formula: R″(C₅R′_(m))₂Me Q_(p) wherein (C₅R′_(m)) is acyclopentadienyl or substituted cyclopentadienyl; R′ is hydrogen orhydrocarbyl radical having from 1 to 20 carbon atoms, each R′ may be thesame or different; R″ is an alkylene radical having 1-4 carbon atoms, asilicon hydrocarbyl compound, a germanium hydrocarbyl compound, an alkylphosphine, or an alkyl amine, and R″ is a bridge between the two(C₅R′_(m)) rings; Q is a hydrocarbon radical such as an aryl, alkyl,alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is ahalogen; Me is a group 4b, 5b or 6b metal designated in the PeriodicTable of Elements; 0≦m≦4; and 0≦p≦3; and (b) changing the R′ group onthe cyclopentadienyl rings.
 33. The method of claim 32 wherein the R′ ischanged to include hydrogen.
 34. The method of claim 32 wherein themetallocene catalyst is selected from the group consisting oftitanocene, zirconocene, and hafnocene.
 35. The method of claim 32wherein the olefin monomer is propylene.
 36. The method of claim 32wherein the metallocene catalyst is a hafnocene.